Xerographic developing system rolls having magnets of different widths

ABSTRACT

A xerographic developing system has rotating rolls in which stationary magnets of different axial widths are located. Magnetic developer is attracted to these rolls and the developer band width is controlled by the width of the magnets. The rolls may be transport rolls or developer rolls. When this concept is employed for transport rolls, a much larger sump capacity may be utilized since the developer band width can be controlled by varying the sizes of the magnets to keep the developer at the outer edges of the developer sump moving inwards to the developer zone. When this concept is employed for developer rolls, compensation is provided for spreading of the developer band and thereby loss of developer when the developer band is transported from one development roll in a magnetic brush system to another development roll either directly or by an intermediary transport roller.

This is a continuation of application Ser. No. 354,598, filed 4/26/73and now abandoned.

This invention relates to magnetic developer transport systems andmagnetic brush development systems.

More specifically, this invention relates to a magnetic developertransport system which controls the developer band width duringtransport thereof.

One application of the invention is for magnetic developer transportsystems for a cascade development system.

Another application of the invention is for a magnetic transport systemfor a magnetic brush developer system.

Still another application of the invention is for a transport assemblywhich transports developer from one magnetic brush developer roll toanother magnetic brush developer roll.

It is usually desirable to have as much developer capacity as possiblein a developer sump since the more capacity that a sump has, the lessfrequent that a copying machine must be serviced to replace olddeveloper with new developer.

It is an object of this invention to provide a developer transportsystem which will permit the use of large capacity developer sumps.

A problem with a magnetic brush development system has been spreading ofa toner band on the magnetic brush when the developer is passed betweena nip formed by the magnetic brush and a photoreceptive surface and alsobetween the nip of a magnetic brush and a transport roll in a multi-rolldeveloper brush system whereby some of the developer is forced out ofthe development zone and is therefore no longer available for developingan image during that cycle.

It is another object of this invention to provide a multi-magneticdeveloper roll system with means which will allow for spreading of adeveloper band on a magnetic developer roll and on an intermediatetransport roll and yet retain all of the developer and transport thesame at a proper width to another magnetic developer brush so that allof the developer may be used for developing an image during that cycle.

Other objects of this invention will become apparent from the followingdescription with reference to the drawings wherein:

FIG. 1 is a schematic view of a xerographic copying system illustratingin particular a magnetic roll transport system;

FIG. 2 is a view of the transport system of FIG. 1 flattened out toillustrate a developer transport path and the relative width of magnetmembers in the transport system;

FIG. 3 is a view along section line 3-3 of FIG. 1; and

FIG. 4 is a view of a schematic brush developer system in which theconcept of the invention is incorporated.

This invention relates to well-known xerographic copier systems. Suchsystems utilize a photoconductive drum or belt having arranged around itan imaging station, a developing station, a transfer station, a fusingstation, and a cleaning station, all of which are wellknown to thoseskilled in the art.

Referring to FIG. 1, there is illustrated a development station whichcomprises a drum 10, having a photoconductive surface 11 thereon, adeveloper sump 12 having developer particles 14 therein, a pair ofrotatable cylindrical transport rolls 16 and 18, and a developmentelectrode 20. The term "developer" as used in this specification and inthe claims refer to either xerographic carrier particles havingferromagnetic properties mixed with xerographic toner particles orxerographic toner particles per se having ferromagnetic properties.Located within the transport roll 16 are a plurality of stationarycircumferentially arranged permanent magnets 22, 24, 26 and 28 which arefixed to the developer housing.

Located within the transport roll 18 are stationary circumferentiallyarranged permanent magnets 30, 32 and 34. These permanent magnets are inthe form of bars which extend generally parallel to the axis about whichits respective transport roll rotates.

Referring to FIG. 2, the rolls 16 and 18 are depicted in a flattened outposition to illustrate the developer band width during transportthereof. The rolls have also been partially cut away to show therelative lengths of the permanent magnets surrounded thereby. It can beseen that magnets 22 and 24 are the longest and are the same length,magnet 26 is shorter, magnets 28 and 30 are the same length but shorterthan magnet 26 and magnets 32 and 34 are the same length but shorterthan magnets 28 and 30 and correspond to the development zone width. Themagnets are positioned in such a manner and are of such a strengthrelative to each other that the developer particles will form a widthcorresponding to substantially the length of the magnet when the tonerparticles are transported by their respective roller to a positionadjacent to the particular magnet. This means that toner particles ontransport roller 16 which are adjacent to the magnet 22 will have a bandwidth equal to the length of the magnet 22 and as the roller carriesthat band into the field of magnet 24 the band will remain the samewidth. When the roller 16 carries the same developer band within thefield of magnet 26 the band width will narrow to the length of magnet 26and then as the band is transported within the field of magnet 28 theband width will narrow to the length of the magnet 28. As the band istransported across the magnet 28 into the field of magnet 30, the bandof toner particles will be attracted to the roller 18 from the roller 16where the toner particles assume a band width on the roller 18equivalent to the length of the magnet 30 which is the same length asmagnet 28. Thereafter the roller 18 transports the same toner band tothe field of magnet 32 wherein the toner band width narrows to thelength of magnet 32 and thereafter the toner particle layer is carriedwithin the field of magnet 34 and remains the same width since magnet 34is the same length as magnet 32. The transport roller 18 continues torotate the band of developer out of the field of magnet 34 to a releasepoint 35 whereby the developer is no longer held onto the roll 18 by themagnet 34 and then falls by centrifugal force and gravity into the spacebetween the electrode 20 and the photoreceptor 10 whereby the developerwill cascade over the photoconductor surface 11 to develop anelectrostatic latent image thereon.

Magnet 22 is positioned in such a manner that it will attract theresidual magnetic developer to the roll 16 thereby acting as a pickoffmagnet. Magnet 24 is positioned to attract additional developer to theroll 16 from the developer sump while the remaining magnets arepositioned for transporting the developer to the release point 35.

As the developer band decreases, the layer of toner at the edges of theband builds up to a thickness greater than the layer between the edgesas shown in FIG. 3. A scraper blade 36 is positioned adjacent the roller18 in such a manner to scrape off the excess developer from the edgeswhereby a uniform layer is carried to the release point 35. The edgelayer which is scraped off by the scraper 36 falls back into thedeveloper sump at a position which corresponds axially with the ends ofthe magnets 34. From this it can be seen that developer which was pickedup in an axial position which corresponds with the ends of the magnets22 and 24 has now been moved inwardly to an axial position whichcorresponds with the development zone width. Thus, this system keepsdeveloper moving from the axial ends of the sump housing to a positionwhere it can be utilized in image development.

In cascade development, it is known that developer is dumped onto thephotoconductive surface over a width that corresponds to the developmentzone but as the developer cascades downwards over the photoconductivesurface, the developer width expands beyond the width of the developmentzone thus requiring a sump which is wider than the development zone. Thedeveloper which is located in the end of the housing, which correspondsto a dimension beyond the width of the development zone, must be mixedand kept moving into the development zone in order that the maximumcapacity of the sump or developer sump is utilized. It follows that withthe system of this invention, it is possible to construct developersumps which are much wider than development zones since one canconstruct and design the magnets to be of such lengths and strengths tonarrow the developer band to the width of the development zone at therelease point. With this additional developer sump capacity, a copiermay be operated for a much longer period of time without having toreplenish developer.

Referring to FIG. 4, there is illustrated a magnetic brush developmentsystem comprising a photoconductor belt 100, a developer sump 102containing magnetic developer particles 104 therein, transport rolls 106and 108, a first development roll 110 and an upper development roll 112,and a transport roll 114 which is located between the development rolls.Located within the transport roll 106 are permanent magnet bars 116, 118and 120. Located within the transport roll 108 are permanent magnet bars122, 124, and 126 and located within the developer roll 110 arestationary permanent magnet bars 128, 130 and 132. Stationary permanentmagnet bars 134, 136 and 138 are located within the transport roll 114and stationary permanent magnet bars 140, 142 and 144 are located withinthe developer roll 112. A scraper member 146 is located adjacent thedeveloper roll 112 and a scraper member 148 is located adjacent thedeveloper roll 110 to scrape off excess developer on the respectiverolls and direct the same back to the sump 102. The transport rolls 106and 108 operate in the same manner as the rolls 16 and 18 in theembodiment of FIG. 1. The magnet 116 is positioned to attract developerfrom the sump to the surface of the roll 106 and is of a length which isgreater than the width of the development zone. Magnets 120, 122, 124and 126 are progressively shorter than magnet 16 to narrow the developerband attracted to the roll 106 by the magnet 116 to a width equal to thedevelopment zone which is the width of magnet bar 126. The developerband is transferred to the magnetic brush as it comes within the fieldof the magnet 128 and since the band has already been reduced to thedevelopment zone width, the magnets 128 and 130 may be of equal length.

As described previously, developer builds up at the ends of thedeveloper band as it becomes narrowed and therefore the scraper 148 isutilized to scrape off the excess developer at the edges of thedeveloper band which falls back into the developer sump.

When developer passes through a nip between two rolls such as betweenthe photoconductor 100 and developer roll 110, the developer roll 110and transport roll 114, and the transport roll 114 and the developmentroll 112, the developer band widens whereby developer is forced eitherout of the development zone or off the ends of the developer rolls. Inorder to compensate for and prevent this from happening, the magnets 132and 134 may be longer than the development zone width to keep thedeveloper on the rolls. Magnets 136 and 138 may be decreasingly shorterin length than magnet 134 so when the developer band is passed throughthe nip between the transport roll 114 and the developer roll 112 thedeveloper band will spread to the width of the developer zone thusretaining all the developer for presentation by the developer roll 112to the latent image.

If transport roll 114 is utilized as a developer roll instead of atransport roll, the width of the magnets of each roll could be adjustedto compensate for widening of the developer band as the band passesthrough the nip between the photoconductor 100 and the respectivedeveloper roll to avoid developer loss and thus retain all the developerfor presentation to the latent image.

In summary, it can be seen that in accordance with the principles ofthis invention, the developer band width can be controlled by varyingthe sizes of the magnets to keep the developer at the outer edges of thedeveloper sump moving inwards to the developer zone. It can also beutilized to compensate for spreading of the developer band and therebyloss of developer when the developer band is transported from onedevelopment roll in a magnetic brush system to another development rolleither directly or by an intermediary transport roller.

It is obvious that the concept of this invention may be applied tocontinuous webs rather than the transport or developer rollersdescribed.

It should be understood that to carry out the principles of theinvention the magnets can be designed to be any length and adjacentmagnets may either vary in length or be the same length depending on theresults desired and the space available to obtain such results. The maincriteria is to design the magnets in such a manner to shape thedeveloper band width in accordance with desired results.

What is claimed is:
 1. In a developer system: developer havingferromagnetic properties, at least two endless rotatable members havingsaid developer said members about a respective axis, first magneticmeans for attracting developer from one of said rotatable members andholding the same on the other of said rotatable members, second magneticmeans for attracting and holding said developer on said one rotatablemember until the developer is rotated within the field of said firstmagnetic means, said first magnetic means including at least onepermanent stationary magnet member extending in a generally axialdirection surrounded by said other rotatable member, said secondmagnetic means including at least one permanent stationary magnet memberextending in a generally axial direction surrounded by said onerotatable member, one of said magnet members being longer than the otherof said magnet members with the ends of said longer magnet memberextending in an axial direction beyond the ends of the shorter magnetmember whereby the developer within the field of the longer of saidmagnet members will extend an axial width on its respective rotatablemember corresponding substantially to the width of the longer magnetmember and the developer within the field of the shorter magnet memberwill extend an axial width on its respective rotatable membercorresponding substantially to the width of the shorter magnet member.2. The structure as recited in claim 1 further comprising a developersump containing said developer therein, said one rotatable member beinglocated that a portion thereof contacts the developer in said sump, saidlonger magnet member being surrounded by said one rotatable member andbeing located to attract developer from said sump to said one rotatablemember.
 3. The structure as recited in claim 2 further comprising aphotoreceptive surface having an electrostatic image thereon, said otherrotatable member being so located that upon release of developertherefrom, the developer will cascade over the electrostatic latentimage to develop the same, said first magnetic means holding saiddeveloper on said other rotatable member until the developer is rotatedto a position where it can be released and cascaded over the latentimage.
 4. The structure as recited in claim 1 further comprising aphotoreceptor surface having an electrostatic latent image thereon, saidone rotatable member being so located to present developer to the latentimage to develop the same.
 5. The structure as recited in claim 1wherein said rotatable members are cylindrical rollers.
 6. The structureas recited in claim 1 wherein the developer comprises carrier and tonerparticles.
 7. The structure as recited in claim 1 wherein the developercomprises toner particles having ferromagnetic properties.
 8. In adeveloper system: developer having ferromagnetic properties, an endlessrotatable member having said developer thereon, means for rotating saidmember about a given axis, magnetic means for attracting and holdingsaid developer on said member for a given degree of rotation through adeveloper path, said magnetic means including at least two permanentstationary magnet members extending in a generally axial directionsurrounded by said rotatable member, one of said magnet members beinglonger than the other with the ends of the longer magnet memberextending in an axial direction beyond the ends of the shorter magnetmember, whereby the developer within the field of the longer of saidmagnet members will extend an axial width on said rotatable membercorresponding substantially to the width of the longer magnet member andthe developer within the field of the shorter magnet member will extendan axial width on said rotatable member corresponding substantially tothe width of the shorter magnet member.
 9. The structure as recited inclaim 8 further comprising a developer sump containing said developertherein, said rotatable member being located that a portion thereofcontacts the developer in said sump, said longer magnet being so locatedto attract developer from said sump to said rotatable member, saidshorter magnet being located at another position along the developerpath whereby the developer axial width will be narrowed as the rotatablemember rotates.
 10. The structure as recited in claim 9 furthercomprising a photoreceptive surface having an electrostatic imagethereon, said rotatable member being so located to present developer tothe electrostatic latent image to develop the same, said shorter magnetmember being located at a position along the developer path which isprior to the developer being presented to the latent image, said shortermagnet being substantially the same width as the width of thedevelopment zone for the latent image.
 11. The structure as recited inclaim 8 further comprising a photoreceptor surface having anelectrostatic image thereon, said rotatable member being so located thatupon release of developer therefrom, the developer will cascade over theelectrostatic latent image to develop the same, said magnetic meansholding said developer on said rotatable member until the developer isrotated to a position where it can be released and cascaded over thelatent image.
 12. The structure as recited in claim 8 wherein saidrotatable member is a cylindrical roller.
 13. The structure as recitedin claim 8 wherein a second endless rotatable member having developerthereon is adjacent said endless rotatable member, said second memberadapted to receive developer from said endless rotatable member.
 14. Thestructure as recited in claim 8 wherein the developer comprises carrierand toner particles.
 15. The structure as recited in claim 8 wherein thedeveloper comprises toner particles having ferromagnetic properties. 16.In a development unit for transporting ferromagnetic developer, thecombination comprisingan endless member mounted for rotation about apredetermined axis, and magnetic means disposed within and surrounded bysaid endless member and extending axially of said member for supplyingat least two stationary magnetic fields of different effective axiallengths, said one field being longer than said other field whereby saiddeveloper band width decreases as said member rotates through saidangle.
 17. A system for transporting ferromagnetic developercomprisingmovable developer support means for defining a path ofmovement of said developer, said support means comprising an endlessmember mounted for rotation about a fixed axis, and magnetic meansassociated with said support means for attracting to and holdingdeveloper on said support means in a band having varying widths alongsaid path wherein said magnetic means is stationary and enclosed withinsaid member.
 18. The combination recited in claim 17 wherein saidmagnetic means comprises permanent magnets for generating magneticfields which intersect said support means, said fields having differentaxial effect on said developer.
 19. A development system for areproduction machine comprisinga nonmagnetic conveyor, a storage sumpfor holding a quantity of developer having ferromagnetic properties,means for moving said conveyor along a path through said developmentsystem, said conveyor operative to support developer bands of differingwidths along said path, first magnetic field defining means forestablishing a first field of sufficient strength and extent to holdsaid developer to said conveyor along a first width of said conveyor,and second magnetic field defining means for establishing a second fieldeffective to hold said developer to said conveyor along a second widthof said conveyor, wherein said first and second magnetic field definingmeans are located on the side of said conveyor opposite said developer,and comprise permanent magnets of different lengths.